A Computer Memory Primer

Here is a quick list of the different types of memory found within a typical computer workstation / server.

SRAM (Static RAM) DRAM (Dynamic RAM) DRAM DRAM DRAM DRAM DRAM DRAM DRAM
SIMM SIMM DIMM DIMM DIMM DIMM DIMM RIMM
SDR
SDRAM
DDR(1) SDRAM DDR2 SDRAM DDR3 SDRAM DDR4
SDRAM
2000 2003 2007 2012
32 Bit 32 Bit 64 Bit 64 Bit 64 Bit 64 Bit 64 Bit
1 –> 128 MB
30 Pin 72 Pin 168 Pin 184 Pin 240 Pin 240 Pin (different notch to DDR2) 284 Pin
SO-DIMM = 200 Pin SO-DIMM = 200 Pin (different notch to DDR1) SO-DIMM = 204 Pin
DDR3L is a Low Voltage Version
  • SRAM (Static RAM) is mainly used within the CPU Cache. It is faster, but more expensive to produce than DRAM.
  • DRAM (Dynamic RAM) is essentially Computer Main Memory
  • SIMM = Single Inline Memory Module
  • DIMM = Dual Inline Memory Module. These can be ECC and / or Registered (Buffered) in Servers and High End Workstations. So, “standard” DIMM modules are also known as UDIMM (Unregistered), whilst registered memory is RDIMM
  • ECC = Error Correction Code. An extra “parity” chip on the memory board is used to detect and correct errors. Due to the additional chip (and processing required), ECC RAM is both more expensive and slower than Non-ECC Memory.
  • Registered / Buffered Memory.
  • SDRAM = Synchronous Dynamic Random Access Memory
  • SDR = Single Data Rate
  • DDR = Double Data Rate
  • SO-DIMM = Small Outline Dual Inline Memory Module (Laptop Memory)
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